Scala: join an iterable of strings

Question

How do I "join" an iterable of strings by another string in Scala?

val thestrings = Array("a","b","c")
val joined = ???
println(joined)

I want this code to output a,b,c (join the elements by ",").

@scala_newbie I think your question was downvoted, 'cause some people think it lacks of research effort. — om-nom-nom, Nov 23 '12 at 17:00

score 505 · Accepted Answer · edited Nov 29 '19 at 10:31

505

How about mkString ?

theStrings.mkString(",")

A variant exists in which you can specify a prefix and suffix too.

See here for an implementation using foldLeft, which is much more verbose, but perhaps worth looking at for education's sake.

edited Nov 29 '19 at 10:31

Magnus Reftel

answered Nov 23 '12 at 12:49

Brian Agnew

Note that the foldLeft implementation assumes a non-empty list – Ferdy Oct 24 '15 at 21:20
8

Thanks! In case anyone wants to enclose string elements in quotes, mkString is also helpful: theStrings.mkString("'", "','", "'") – Niko Gamulin Aug 23 '16 at 13:20
1

@Frawr That page links to a bunch of examples https://oldfashionedsoftware.com/2009/07/30/lots-and-lots-of-foldleft-examples/ which includes an implementation that uses pattern matching for the empty list (Nil) case. Modifying it to mimic mkString would be like this: `def mkFoldLeftString[A](list:List[String], delim:String = ","): String = list match { case head :: tail => tail.foldLeft(head)(_ + delim + _) case Nil => "" }` – Davos Jul 11 '17 at 14:37
3

The langref.org link is dead – Floegipoky Mar 09 '18 at 22:43

1 Answers1